The invention generally relates to a rewritable fuse memory.
It is often desirable to permanently store information or form permanent connections in a semiconductor integrated circuit after the integrated circuit has been fabricated. A fuse is a programmable storage device that may be used to accomplish these goals. More specifically, the integrated circuit may have a number of fuses that collectively form the storage elements of a fuse memory. The fuse memory may be programmed to configure the integrated circuit for purposes of adjusting operating parameters (an operating frequency, for example) of the integrated circuit, designating defective memory cells, indicating a die identification number, indicating program instructions, indicating configuration information, etc.
A typical fuse has either a low resistance state or a high resistance state, and it is through these states that the fuse indicates respective logical states. For example, a typical fuse may exhibit a low resistance state (indicative of a logic zero, for example) before being programmed, and after being programmed, the fuse may be “blown” so that the fuse exhibits a high resistance state (indicative of a logic one, for example). A type of fuse called an antifuse may exhibit the opposite properties: a high resistance state before being programmed and a low resistance state after being programmed.
Fuses typically are one time programmable (OTP) devices, a designation that means once programmed, the fuses cannot be reprogrammed. Although configuration and option information stored in a memory of the integrated circuit may be considered “permanent” relative to the life of the integrated circuit, it may be desirable to change information at least once. For example, an original equipment manufacturer (OEM) may want to overwrite information stored on the integrated circuit by the fabricator of the circuit. Therefore, fuse memories are often not used if potential reprogramming of the fuse memory is contemplated. Other types of memories (an electrically erasable programmable read only memory (EEPROM) or a flash memory, as examples) may alternatively be used. However, these memories may be relatively more expensive and may consume more die area than a fuse memory.
Thus, there is a continuing need for an arrangement and/or technique to improve upon memory storage for an integrated circuit.